From 4c43f23aacb1c65b88cdd4602ae46f1540422a3b Mon Sep 17 00:00:00 2001
From: David Kastrup <dak@gnu.org>
Date: Thu, 11 Jun 2015 11:28:49 +0200
Subject: [PATCH] Add \override and \revert music functions usable from Scheme

---
 ly/music-functions-init.ly | 52 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 52 insertions(+)

diff --git a/ly/music-functions-init.ly b/ly/music-functions-init.ly
index 6ccecd6581..4e7e1d4105 100644
--- a/ly/music-functions-init.ly
+++ b/ly/music-functions-init.ly
@@ -933,6 +933,33 @@ ottava =
    (make-music 'OttavaMusic
                'ottava-number octave))
 
+#(ly:expect-warning
+  (ly:translate-cpp-warning-scheme "identifier name is a keyword: `%s'")
+  "override")
+override =
+#(define-music-function (grob-property-path value)
+   (symbol-list? scheme?)
+   (_i "Set the grob property specified by @var{grob-property-path} to
+@var{value}.  @var{grob-property-path} is a symbol list of the form
+@code{Context.GrobName.property} or @code{GrobName.property}, possibly
+with subproperties given as well.  Because @code{\\override} is a
+reserved word with special syntax in LilyPond input, this music
+function will generally only be accessible from Scheme.")
+   (let ((p (check-grob-path grob-property-path (*parser*) (*location*)
+                             #:default 'Bottom
+                             #:min 3)))
+     (if p
+         (context-spec-music
+          (make-music 'OverrideProperty
+                      'symbol (cadr p)
+                      'origin (*location*)
+                      'grob-value value
+                      'grob-property-path (cddr p)
+                      'pop-first #t)
+          (car p))
+         (make-music 'Music))))
+
+
 overrideTimeSignatureSettings =
 #(define-music-function
    (time-signature base-moment beat-structure beam-exceptions)
@@ -1302,6 +1329,31 @@ usually contains spacers or multi-measure rests.")
                'element main-music
                'quoted-music-name what))
 
+#(ly:expect-warning
+  (ly:translate-cpp-warning-scheme "identifier name is a keyword: `%s'")
+  "revert")
+revert =
+#(define-music-function (grob-property-path)
+   (symbol-list?)
+   (_i "Revert the grob property specified by @var{grob-property-path} to
+its previous value.  @var{grob-property-path} is a symbol list of the form
+@code{Context.GrobName.property} or @code{GrobName.property}, possibly
+with subproperties given as well.  Because @code{\\revert} is a
+reserved word with special syntax in LilyPond input, this music
+function will generally only be accessible from Scheme.")
+   (let ((p (check-grob-path grob-property-path (*parser*) (*location*)
+                             #:default 'Bottom
+                             #:min 3)))
+     (if p
+         (context-spec-music
+          (make-music 'RevertProperty
+                      'symbol (cadr p)
+                      'origin (*location*)
+                      'grob-property-path (cddr p))
+          (car p))
+         (make-music 'Music))))
+
+
 relative =
 #(define-music-function (pitch music)
    ((ly:pitch?) ly:music?)
-- 
2.39.5